WO2005094121A1

WO2005094121A1 - Piezoelectric acoustic element, acoustic device and portable terminal device

Info

Publication number: WO2005094121A1
Application number: PCT/JP2004/019010
Authority: WO
Inventors: Yasuharu Onishi; Yasuhiro Sasaki; Nozomu Toki
Original assignee: Nec Corporation
Priority date: 2004-03-25
Filing date: 2004-12-20
Publication date: 2005-10-06
Also published as: JP4662072B2; CN1926917A; US20070177747A1; US7860259B2; JPWO2005094121A1; CN1926917B

Abstract

A piezoelectric acoustic element (1) comprising a hollow casing (5) having an opening (3), a piezoelectric element (7) which is disposed in the casing (5) and bends when a voltage is applied thereto, and a diaphragm (8) provided at the opening (3) of the casing (5). The piezoelectric element (7) and the diaphragm (8) are joined with each other via an elastic vibration transmitting member (9).

Description

Specification

Piezoelectric acoustic element, acoustic device, and portable terminal device

Technical field

The present invention relates to a piezoelectric acoustic device using a piezoelectric element as a vibration source, an acoustic device including a piezoelectric acoustic device using a piezoelectric element as a vibration source, and a portable terminal device.

Background art

A piezoelectric acoustic element using a piezoelectric element as a vibration source has various advantages such as small size, light weight, low power consumption, and no leakage magnetic flux, and is therefore expected as an acoustic component of a portable terminal device. In particular, since the mounting volume can be significantly reduced as compared with a conventional electromagnetic acoustic element, it is considered to be one of the important technologies for further miniaturizing a mobile phone.

[0003] However, the sound source of the piezoelectric acoustic element is a diaphragm that bends as the piezoelectric element deforms. Therefore, in order to secure a general sound pressure level required for music reproduction, the diaphragm must be bent to a certain degree or more, and a large diaphragm is required. For example, a conventional piezoelectric acoustic element requires a diaphragm with a diameter of 20 mm to obtain a sound pressure of 90 dB when a voltage of 1 V is applied to the piezoelectric element. As a result, the advantages of the piezoelectric acoustic device, such as small size and light weight, were lost.

Next, the frequency characteristics of a conventional piezoelectric acoustic device will be described. Piezoelectric acoustic devices have the following problems.

(1) The fundamental resonance frequency appears in the audible range.

(2) It has a frequency characteristic that generates a prominent sound pressure near the resonance frequency.

(3) Since the ceramic used as the piezoelectric material of the piezoelectric element has high rigidity, the basic resonance frequency increases, and sufficient sound pressure cannot be obtained in a low frequency range.

[0005] In order to faithfully reproduce the original sound, it is necessary to adjust the basic resonance frequency to 500 [Hz] or less. Therefore, Japanese Patent Application Laid-Open No. 2-127448 discloses a technique for improving the frequency characteristics by using a carbon plate (expanded graphite plate) for the diaphragm. It is also known that the frequency characteristics can be improved to some extent by making the diaphragm elliptical. Next, the frequency sound pressure characteristics of the conventional piezoelectric acoustic device will be described. As described above, the conventional piezoelectric acoustic device uses the piezoelectric device as a vibration source. As the piezoelectric material of the piezoelectric element, a ceramic material or the like having a small loss of mechanical energy in elastic vibration is generally used. For this reason, a very high sound pressure can be obtained near the resonance point, but in a frequency range other than the resonance point, an uneven frequency sound pressure characteristic having a large amplitude change is obtained. If the amplitude change of the frequency sound pressure characteristic is large, only the sound of the specific frequency is emphasized and the sound quality is deteriorated. Thus, Japanese Utility Model Application Laid-Open No. 63-81495 discloses a technique for flattening frequency sound pressure characteristics by embedding a piezoelectric vibrator in a soft foam. Also, Japanese Patent Application Laid-Open No. 60-208399 discloses a technique for flattening the frequency sound pressure characteristics by supporting the outer edge of a thin acoustic element with a foam having an adhesive layer formed on the surface. I have.

Patent Document 1: JP-A-2-127448

Patent Document 2: Japanese Utility Model Application Laid-Open No. 63-81495

Patent Document 3: JP-A-60-208399

Disclosure of the invention

Problems to be solved by the invention

[0007] The above-mentioned problems (1) and (2) can be improved by using the technology disclosed in Japanese Patent Application Laid-Open No. 2-127448 or an elliptical diaphragm. Is greatly deteriorated. Further, by using the techniques disclosed in Japanese Utility Model Application Laid-Open No. 63-81495 and Japanese Patent Application Laid-Open No. 60-208399, the frequency and sound pressure characteristics of the piezoelectric acoustic element can be reduced to some extent. However, the frequency and sound pressure characteristics cannot be improved to an extent sufficient to faithfully reproduce the original sound. In addition, the overall sound pressure characteristic is deteriorated. As described above, it has been difficult to realize a piezoelectric acoustic device having good frequency characteristics and frequency sound pressure characteristics, while having low power consumption in the j-type.

Means for solving the problem

[0008] An object of the present invention is to realize a piezoelectric acoustic element that is small and lightweight, has low power consumption, and has excellent acoustic characteristics.

[0009] The piezoelectric acoustic element of the present invention that achieves the above object has at least one opening. It has a hollow housing, a piezoelectric element provided inside the housing, which bends when a voltage is applied, and a vibrating film provided at an opening of the housing, wherein the piezoelectric element and the vibrating film are elastic. When the piezoelectric element is bent, the vibration film vibrates to generate a sound. One or both ends in the longitudinal direction of the piezoelectric element can be fixed to the inner surface of the housing directly or via a support member. The support member may have elasticity or may not have elasticity.

[0010] Two or more vibration films and vibration transmission members are provided, respectively, and at least one of the thickness, material, and dimensions of the two or more vibration films and Z or the vibration transmission members can be different from each other. The two vibrating films can be arranged to face each other with the piezoelectric element interposed therebetween, and the two vibrating films can be joined to the piezoelectric element via separate vibration transmitting members. An elastic plate may be joined to the piezoelectric element, and the elastic plate joined to the piezoelectric element may be joined to the vibration film via a vibration transmitting member.

[0011] A piezoelectric element having a laminated structure in which conductor layers and piezoelectric material layers are alternately stacked can be used as a vibration source of the piezoelectric acoustic element of the present invention. Further, a panel can be used as the vibration transmitting member. Any one of polyethylene terephthalate film, polyetherenosulfone film, polyester film and polypropylene film can be used for the diaphragm.

[0012] The acoustic device or the portable terminal device of the present invention is equipped with the piezoelectric acoustic element of the present invention.

In the piezoelectric acoustic device of the present invention, since the piezoelectric element, which is the vibration source, and the vibration film are joined via the elastic vibration transmitting member, the bending action of the piezoelectric element and the elasticity restoration of the vibration transmitting member are achieved. The vibrating membrane vibrates greatly in synergy with the action. Therefore, a sufficient sound pressure can be obtained by vibrating the vibrating membrane largely even if the bending of the piezoelectric element itself is small. Also, a sufficient sound pressure can be obtained by using a vibrating membrane having a small area. As a result, a piezoelectric acoustic device that is excellent in sound pressure characteristics and frequency characteristics while being thin and small, low power consumption, and low cost is realized. In addition, if a piezoelectric acoustic element having such an effect is adopted as an acoustic component of an acoustic device or a portable terminal device, the size, thickness, power consumption, and sound quality of the device can be reduced. [0014] The above and other objects, features and advantages of the present invention will become apparent by reference to the following description and accompanying drawings which show an example of the present invention.

Brief Description of Drawings

FIG. 1A is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Embodiment 1.

FIG. 1B is a longitudinal sectional view showing a vibration displacement state of the vibration film.

FIG. 1C is a longitudinal sectional view showing a vibration displacement state of the vibration film.

FIG. 2 is a longitudinal sectional view showing a structure of a piezoelectric acoustic device of Embodiment 2.

FIG. 3 is a longitudinal sectional view showing a structure of a piezoelectric acoustic device of Embodiment 3.

FIG. 4 is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Embodiment 4.

FIG. 5 is a longitudinal sectional view showing a structure of a piezoelectric acoustic device of Embodiment 5.

FIG. 6 is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Embodiment 6.

FIG. 7 is an exploded perspective view showing a structure of a piezoelectric element included in the piezoelectric acoustic element of Embodiment 7.

FIG. 8 is a longitudinal sectional view showing the structure of a piezoelectric acoustic device of Embodiment 8.

FIG. 9A is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Example 1.

FIG. 9B is a transverse sectional view showing the structure of the piezoelectric acoustic device of Example 1.

FIG. 10 is an exploded perspective view showing the structure of the piezoelectric element shown in FIG. 9.

FIG. 11 is a side view of the vibration transmitting member shown in FIG. 9.

FIG. 12A is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Example 2.

FIG. 12B is a transverse sectional view showing the structure of the piezoelectric acoustic device of Example 2.

FIG. 13A is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Example 3.

FIG. 13B is a transverse sectional view showing the structure of the piezoelectric acoustic device of Example 3.

FIG. 14 is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Example 4.

FIG. 15 is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Example 5.

FIG. 16 is an exploded perspective view showing the structure of the piezoelectric element shown in FIG.

FIG. 17 is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Example 6.

18 is an enlarged perspective view of the piezoelectric element and the elastic plate shown in FIG.

FIG. 19 is a longitudinal sectional view showing the structure of the piezoelectric acoustic device of Example 7. FIG. 20 is an enlarged perspective view of the piezoelectric element and the elastic plate shown in FIG. 19.

FIG. 21 is a longitudinal sectional view showing the structure of a piezoelectric acoustic device of Example 8.

FIG. 22 is an enlarged perspective view of the panel shown in FIG. 21.

FIG. 23 is a longitudinal sectional view showing the structure of the acoustic element of Comparative Example 1.

FIG. 24 is a longitudinal sectional view showing the structure of an acoustic element of Comparative Example 2.

FIG. 25 is a longitudinal sectional view showing the structure of an acoustic element of Comparative Example 3.

FIG. 26 is a longitudinal sectional view showing the structure of an acoustic element of Comparative Example 4.

Explanation of symbols

1 Piezoelectric acoustic element

2 Bottom

3 Opening

5 housing

6 Support members

7 Piezoelectric element

8 vibrating membrane

9 Vibration transmission member

10 Top

11 Ceiling surface

12 space

13 bottom

15 Elastic plate

16 Lower insulating layer

17 Upper insulating layer

18 Conductive layer

19 Piezoelectric material layer

20 Electrode pad

21 Foam rubber

22 Upper member 23 Lower member

25 leg members

30 Acoustic element

31 housing

32 Piezoelectric element

33 Support members

34 bottom

35 holes

36 Connecting member

37 diaphragm

38 permanent magnet

39 Voice Call

40 diaphragm

41 Electrode terminal

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1)

Hereinafter, an example of an embodiment of the piezoelectric acoustic device of the present invention will be described. 1A to 1C are longitudinal sectional views showing a schematic structure of the piezoelectric acoustic device of the present example. As shown in FIG. 1A, the piezoelectric acoustic device 1 of the present example has a hollow housing 5 having an opening 3 formed on a bottom surface 2 and one end (fixed end) of the housing 5 via a support member 6. It has a piezoelectric element 7 fixed to the inner surface and a vibrating membrane 8 stretched over the opening 3 of the housing 5. The other end (free end) of the piezoelectric element 7 is joined to the vibration film 8 via the vibration transmission member 9. The support member 6 and the vibration transmitting member 9 are both formed of an elastic material. A space 12 having a height (h) is provided between the upper surface 10 of the piezoelectric element 7 and the ceiling surface 11 of the housing 5.

The piezoelectric element 7 to which the voltage is applied repeats the expansion and contraction movement, and the expansion and contraction movement of the piezoelectric element 7 is transmitted to the vibration film 8 via the vibration transmission member 9, and the vibration film 8 vibrates up and down. More specifically, as shown in FIG. 1B, the piezoelectric element 7 to which the forward or reverse voltage is applied bends upward with the fixed end as a fulcrum, and deflects the vibrating membrane 8 in the same direction. At this time, space 12 The piezoelectric element 7 serves as a clearance for displacing the piezoelectric element 7 upward. On the other hand, as shown in FIG. 1C, the piezoelectric element 7 to which the reverse or forward voltage is applied bends downward with the fixed end as a fulcrum, and deflects the vibrating membrane 8 in the same direction. As described above, when the AC voltage is applied to the piezoelectric element 7, the vibrating membrane 8 continuously radiates (vibrates) up and down, and a sound is generated. Here, in the piezoelectric acoustic element 1 of the present example, the piezoelectric element 7 and the vibration film 8 are joined via the elastic vibration transmitting member 9. Therefore, the vibration transmitting member 9 is elastically deformed in accordance with the expansion and contraction of the piezoelectric element 7, and a repulsive action is generated. As a result, the expansion and contraction movement of the piezoelectric element 7 is promoted, the amount of vibration displacement of the vibration film 8 is increased, and the sound pressure is improved. Further, since the weight of the piezoelectric element 7 to which the vibration transmitting member 9 is joined is increased, greater inertia acts when the piezoelectric element 7 expands and contracts, and the basic resonance frequency of the generated sound is reduced. Since the solid end of the piezoelectric element 7 is fixed to the housing 5 via the elastic supporting member 6 and the free end is joined to the vibration film 8 via the elastic vibration transmitting member 9, Even if the housing 8 receives an impact due to a drop or the like, most of the impact is absorbed by the support member 6 and / or the vibration transmitting member 9, and the piezoelectric element 7 is prevented from being damaged.

The piezoelectric element 7 shown in FIG. 1 has a layer structure in which a lower insulating layer, a lower electrode layer (conductor layer), a piezoelectric material layer, an upper electrode layer (conductor layer), and an upper insulating layer are sequentially stacked. When zirconate / lead zirconate titanate is used as the material of the piezoelectric material layer, warpage after ceramic sintering can be reduced, and the reliability as a piezoelectric element improves. Further, a flattening step such as polishing after ceramic sintering can be omitted, which contributes to a reduction in manufacturing cost. Also, when silver or silver / palladium alloy is used as the material of the electrode layer, the sintering strain during the integral sintering of the electrode layer and the piezoelectric material layer is reduced, so that the piezoelectric element is manufactured by integral sintering. It is easier to do. However, existing materials other than the above materials can be appropriately selected and used as the material of the piezoelectric material layer and the electrode layer.

[0020] A conventional piezoelectric acoustic element generates an emphasized sound at a specific frequency. This is because Q is high when a piezoelectric acoustic element is considered equivalent to an electric circuit element. Therefore, if the vibration film 8 shown in FIG. 1 is formed of a material having a low Q, the Q of the piezoelectric acoustic element can be suppressed, and the frequency can be made equal. Further, if the vibrating film 8 is formed of a material having high durability against displacement operation, a high sound pressure can be obtained. In addition, materials that are easy to process If the vibrating film 8 is formed by this, the variation in the film thickness is reduced and the quality is stabilized. Considering the above items comprehensively, polyethylene terephthalate film (PET film)

) Or a polypropylene film (PP film) is suitable as the material of the diaphragm 8.

(Embodiment 2)

Next, another example of the embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 2 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device of the present example. As shown in FIG. 2, the basic structure of the piezoelectric acoustic device 1 of the present example is the same as that of the piezoelectric acoustic device of the first embodiment. There are two differences. One is that the fixed end of the piezoelectric element 7 is fixed to the inner surface of the housing 5 via a support member 6 having no elasticity. Another is that the free end of the voltage element 7 is joined to the diaphragm 8. In the piezoelectric acoustic device 1 shown in FIG. 1, an arbitrary position between the substantially center of the piezoelectric device 7 in the longitudinal direction and a free end is joined to the vibration film 8. In the piezoelectric element 7 having the fixed end fixed to the housing 5, the free end has the largest displacement. Accordingly, by joining the free end to the vibrating membrane 8, it is possible to more effectively vibrate the vibrating membrane 8. That is, the piezoelectric acoustic element 1 of the present example has an advantage that a sufficient sound pressure can be ensured even when the area of the diaphragm 8 is small.

From the above description, it can be understood that if the piezoelectric element 7 is made longer, the amount of fluctuation of the free end is further increased, and the vibration film 8 can be vibrated more. Further, it can be understood that by making the length of the piezoelectric element 7 and the area of the vibrating membrane 8 a suitable combination, it is possible to reduce the size of the piezoelectric acoustic element while ensuring the required sound pressure.

(Embodiment 3)

Next, still another example of the embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 3 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device of this example. As shown in FIG. 3, the basic structure of the piezoelectric acoustic device 1 of the present example is the same as that of the piezoelectric acoustic device 1 of the first embodiment. The difference is that both ends in the longitudinal direction of the piezoelectric element 7 are fixed to the inner surface of the housing 5 via the support members 6a and 6b. The piezoelectric acoustic device 1 of the present example has the same basic structure as the piezoelectric acoustic device of the first embodiment, and has the same operational effects. Further, the piezoelectric acoustic element of the present example is characterized in that both ends in the longitudinal direction of the piezoelectric element 7 are fixed to the inner surface of the housing 5. This has the advantage that the bonding strength between the child 7 and the housing 5 is further improved.

[0024] Further, by making the elastic modulus, the thickness, the area, and the like of the two support members 6a and 6b different from each other, there is an advantage that the basic resonance frequency of the generated sound can be adjusted. In the piezoelectric acoustic device 1 of this example, the longitudinal center of the piezoelectric device 7 is joined to the vibrating membrane 8 by adopting a configuration in which both ends of the piezoelectric device 7 in the longitudinal direction are fixed to the housing 5. ing. However, the joining position between the piezoelectric element 7 and the vibrating membrane 8 is not limited to the illustrated position.

(Embodiment 4)

Next, still another example of the embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 4 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device of this example. As shown in FIG. 4, the basic structure of the piezoelectric acoustic device 1 of the present example is the same as that of the piezoelectric acoustic device of the first embodiment. There are two differences. One is that two independent openings 3a and 3b are formed in the bottom surface 2 of the housing 5, and the vibrating membranes 8a and 8b are stretched in the openings 3a and 3b, respectively. The other is that a single piezoelectric element 7 is bonded to two vibration films 8a and 8b via two independent vibration transmission members 9a and 9b, respectively.

[0026] The piezoelectric acoustic element 1 of the present example has the same basic structure as the piezoelectric acoustic element 1 of Embodiment 1, and has the same operational effects. Further, the piezoelectric element 7 of the present example is characterized in that the piezoelectric element 7 is joined to the two vibrating films 8a and 8b via two independent vibration transmitting members 9a and 9b, respectively. Since sound is generated from the plates 8a and 8b, there is an advantage that a higher sound pressure can be obtained. Further, the sound generated differs depending on the thickness, height, material, etc., of the two vibration transmitting members 9a, 9b, or the thickness, material, etc., of the two vibrating membranes 8a, 8b. There is also an advantage that a resonance frequency can be provided. These advantages mean that the frequency band of reproducible sound can be expanded. In addition, when the housing 5 receives an impact due to a drop or the like, much of the impact is absorbed by the vibration transmitting member and the supporting member, and is not transmitted to the piezoelectric element. This has the same advantage as the piezoelectric acoustic element described above. is there. However, in the piezoelectric acoustic device 1 of the present example having two independent vibration transmitting members 9a and 9b, the impact is dispersed and absorbed by the two vibration transmitting members 9a and 9b, so that the safety is further improved. (Embodiment 5)

Next, still another example of the embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 5 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device of this example. As shown in FIG. 5, the piezoelectric acoustic device 1 of the present embodiment differs from the piezoelectric acoustic device of the fourth embodiment in that vibrating films 8a and 8b are stretched over two openings 3a and 3b formed in a housing 5. And common. The difference is that the two openings 3 a and 3 b are formed on two different surfaces of the housing 5. Note that the single piezoelectric element 7 is bonded to the two vibration films 8a and 8b via two independent vibration transmission members 9a and 9b, which is common to the piezoelectric acoustic element of the fourth embodiment. . Therefore, the operation and effect obtained by this structure are common to the piezoelectric acoustic device of the fourth embodiment. However, in the piezoelectric acoustic element 1 of this example, the vibrating membranes 8a and 8b are arranged above and below (both sides) the piezoelectric element 7, so that the piezoelectric element 7 must be shorter than the piezoelectric acoustic element of the fourth embodiment. Is possible. Further, when the vibration films 8a and 8b have the same area, the space required for disposing the two vibration films 8a and 8b is smaller than that of the piezoelectric acoustic device of the fourth embodiment.

The area of the vibrating membranes 8a and 8b included in the piezoelectric acoustic device 1 shown in FIGS. 4 and 5 is larger than that of the piezoelectric acoustic device 1 (the piezoelectric acoustic device 1 having one vibrating film 8) shown in FIG. Small. However, in the piezoelectric acoustic device 1 shown in FIGS. 4 and 5, since the two vibrating films 8a and 8b vibrate simultaneously, the obtained sound pressure is at the same level as the piezoelectric acoustic device 1 shown in FIG.

(Embodiment 6)

Next, still another example of the embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 6 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device of this example. As shown in FIG. 6, the basic structure of the piezoelectric acoustic device 1 of the present example is the same as that of the piezoelectric acoustic device 1 of the first embodiment. The difference is that an elastic plate 15 is attached to the lower surface of the piezoelectric element 7. The piezoelectric acoustic device 1 of this example has the same basic structure as the piezoelectric acoustic device 1 of the first embodiment, and has the same operational effects.

However, since the apparent rigidity of the piezoelectric element 7 having the elastic plate 15 integrated therewith is lower than that of the same type of piezoelectric element having no elastic plate 15, the amount of displacement accompanying bending increases. . In other words, the piezoelectric element 7 shown in FIG. 6 can make the vibrating film 8 vibrate more greatly than a piezoelectric element of the same type that does not include the elastic plate 15. From this perspective, piezoelectric It is desirable that the thickness of the elastic body 15 occupies 1/8 or more of the total thickness of the element 7 and the thickness of the elastic plate 15. Further, since the piezoelectric element 7 with the elastic plate 15 integrated therein is heavier than a piezoelectric element of the same type without the elastic plate 15, larger inertia acts when the piezoelectric element 7 is bent, which is generated. The fundamental frequency of the sound is further reduced.

Further, if the elastic plate 15 is formed of a material having a large mass such as a metal, a larger inertia acts when the piezoelectric element 7 is bent, and the fundamental frequency is further reduced. This means that by adding an inexpensive elastic plate 15 to the piezoelectric element 7, the displacement of the piezoelectric element 7 and the resonance frequency of the generated sound can be adjusted without changing the size and shape of the expensive piezoelectric ceramic. Means that. As a result, the durability of the piezoelectric element 7 integrated with the elastic plate 15 is improved, and cracks and the like hardly occur. As a material for the elastic plate 15 made of metal, for example, Machiyu is suitable.

If a panel panel having a high elastic coefficient is used for the elastic plate 15, the apparent elasticity of the piezoelectric element 7 increases, and the displacement of the piezoelectric element 7 when a voltage is applied increases. In addition, if slits are provided in the panel panel, the apparent elasticity of the piezoelectric element 7 is further increased, and the bonding area between the panel panel and the piezoelectric element 7 is reduced, thereby facilitating the manufacturing.

(Embodiment 7)

Next, still another example of the embodiment of the piezoelectric acoustic device of the present invention will be described. The basic structure of the piezoelectric acoustic device of this example is the same as that of the piezoelectric acoustic device of the first embodiment. The difference is the structure of the piezoelectric element 7 as a vibration source. FIG. 7 schematically shows the structure of a piezoelectric element included in the piezoelectric acoustic element of this example. The piezoelectric element 7 has a multilayer structure (laminated structure) in which a conductor layer 18 and a piezoelectric material layer 19 are alternately stacked between a lower insulating layer 16 and an upper insulating layer 17. It is known that the piezoelectric element 7 having a multilayer structure as shown in FIG. 7 consumes less power and has a larger vibration displacement amount than the piezoelectric element 7 of the first embodiment. Therefore, the piezoelectric acoustic element of this example has an advantage that a sufficient sound pressure can be obtained with less power. Further, the piezoelectric element 7 having the structure shown in FIG. 7 prevents warpage and deformation during sintering due to the effect of promoting sintering of the conductive layer material during manufacturing. For this reason, high flatness can be obtained without performing a separate flattening process, and the elastic plate 15 and the like shown in FIG. 6 can be joined without gaps.

(Embodiment 8) Next, still another example of the embodiment of the piezoelectric acoustic device of the present example will be described. FIG. 8 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device of the present example. As shown in FIG. 8, the basic configuration of the piezoelectric acoustic device 1 of this example is the same as that of the piezoelectric acoustic device 1 of the first embodiment. The difference is that the vibration transmitting member 9 is a substantially conical coil panel. The piezoelectric acoustic element 1 of the present example has the same basic structure as the piezoelectric acoustic element 1 of the first embodiment, and has the same operational effects. Further, the coil panel 9 repeatedly accumulates and releases energy as the piezoelectric element 7 expands and contracts, thereby promoting the expansion and contraction movement of the piezoelectric element 7. As a result, the piezoelectric acoustic device 1 of this example has an advantage that the vibration displacement of the vibrating membrane 8 is large and the sound pressure is high. In addition, the impact caused by the drop of the casing 5 or the like is absorbed by the coil panel 9, and the breakage of the piezoelectric element 7 is prevented. The coil panel 9 can be replaced with a plate panel or a spiral panel. In any case, by selecting a panel having an appropriate panel coefficient, the vibration of the diaphragm 8 can be maximized and a high sound pressure can be obtained.

(Example 1)

The piezoelectric acoustic device of the present invention will be described in more detail with reference to examples. FIG. 9A is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device 1 of the present example, and FIG. 9B is a transverse sectional view.

In the piezoelectric acoustic device 1 of this example, a piezoelectric device 7 having a structure shown in FIG. 10 is mounted as a vibration source inside a housing 5 made of 0.3 [mm] thick polypropylene resin. The lower insulating layer 16 and the upper insulating layer 17 of the piezoelectric element 7 are 15 [mm] in length, 4 [mm] in width, and 50 [/ im] in thickness. The piezoelectric material layer 19 has a length of 15 [mm], a width of 4 [mm], and a thickness of 300 [/ im]. The thickness of the upper and lower electrode layers (conductor layers) 18 is 3 m]. Therefore, the outer dimensions of the piezoelectric element 7 are 15 [mm] in length, 4 [mm] in width, and about 0.4 [mm] in thickness. The lower insulating layer 16, the upper insulating layer 17, and the piezoelectric material layer 19 are made of a lead dinoleconate titanate-based ceramic, and the electrode layer 18 is made of a silver / palladium alloy (weight ratio 7: 3). ing. Further, the piezoelectric element 7 is manufactured by the Darline sheet method, and is fired at 1100 ° C. in the air for 2 hours. Further, a silver electrode having a thickness of 8 [μm] is formed as an external electrode for electrically connecting the electrode layer 18. Further, the piezoelectric material layer 19 is polarized in the thickness direction by the polarization process. The electrode pad 20 formed on the surface of the upper insulating layer 17 is electrically connected to an 8 [zm] copper foil. Connected. Further, from the electrically connected electrode pads 20, two electrode terminal lead wires having a diameter of 0.2 [mm] are formed through solder portions having a diameter of l [mm] and a height of 0.5 [mm]. Has been withdrawn.

In the piezoelectric acoustic device of this example, a conical coil panel shown in FIG. 11 is used as the vibration transmitting member 9 for joining the piezoelectric device 7 to the vibration film 8. The conical coil panel has a height (h) of 0.4 [mm], a minimum coil radius (R1) of 2 [mm], and a maximum coil radius (R2) of S4 [mm], and is formed by stainless steel wire. ing. Further, as shown in FIG. 9A, the minimum coil radius surface of the coil panel is bonded to the lower surface 13 of the piezoelectric element 7 and the maximum coil radius surface is bonded to the vibration film 8 by an epoxy-based adhesive. Further, the diaphragm 8 shown in FIGS. 9A and 9B is a circular polyethylene terephthalate film having a diameter of 15 [mm] and a thickness of 0.1 [mm].

[0038] As shown in Fig. 9B, the piezoelectric acoustic element 1 of the present example having the above structure has a substantially elliptical planar shape as a whole, and has an overall length (L) of 23 [mm] and an overall width (W). 16 [mm]. The total height (H) is 1.5 [mm] (thickness of diaphragm 8 (0.1 mm) + height of conical coil spring 9 (0.4 mm) + thickness of piezoelectric element 7 (0.4 mm) + The height of the space 12 (0.3 mm) + the thickness of the housing 5 (0.3 mm)).

(Example 2)

Hereinafter, another embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 12A is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device 1 of the present example, and FIG. 12B is a schematic transverse sectional view. In the piezoelectric acoustic device 1 of the present embodiment, the same piezoelectric device 7 as the piezoelectric device of the first embodiment is joined to the vibrating membranes 8a and 8b stretched over two openings 3a and 3b formed on the upper and lower sides of the housing 5. ing. The vibrating membrane 8a stretched over the opening 3a is a polyethylene terephthalate film having a thickness of 0.1 l [mm], and is provided with a piezoelectric element via a conical coil spring (height: 0.4 mm) as the vibration transmitting member 9a. 7 is joined to the upper surface 10. On the other hand, the vibrating membrane 8b stretched over the opening 3b is a polyethylene terephthalate film having a thickness of 0.05 [mm]. 7 is joined to the lower surface 13. However, the diameter (10 [mm]) of the two vibrating membranes 8a and 8b is common.

As shown in FIG. 12B, the piezoelectric acoustic device 1 of the present example has substantially the same shape as the piezoelectric acoustic device of the first embodiment. However, the diaphragms 8a and 8b of the piezoelectric acoustic element 1 of this example Since the diameter is smaller than the vibrating membrane provided in the piezoelectric acoustic device of Example 1 (the area of the vibrating membrane is small), the overall length (L) of the piezoelectric acoustic device 1 of this example is 20 [mm] and the overall width (W ) Is ll [mm]. That is, the piezoelectric acoustic device 1 of the present example is smaller than the piezoelectric acoustic device of the first embodiment. The total height (H) is 1.15 [mm] (thickness of diaphragm 8b (0.05 mm) + height of conical coil spring 9b (0.2 mm) + thickness of piezoelectric element 7 (0.4 mm) + cone Height of coil spring 9a (0.4 mm) + thickness of diaphragm 8a (0.1 mm)).

The housing 8 and the piezoelectric element 7 included in the piezoelectric acoustic element 1 of the present embodiment are the same as those included in the piezoelectric acoustic element of the first embodiment. Further, the conical coil spring included in the piezoelectric acoustic element 1 of this example is the same as the conical coil panel included in the piezoelectric acoustic element of Example 1 except for the size.

(Example 3)

Hereinafter, still another embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 13A is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device 1 of the present example, and FIG. 13B is a transverse sectional view. In the piezoelectric acoustic device 1 of this example, both ends in the longitudinal direction of the piezoelectric device 7 are joined to the foam rubber 21, the foam rubber 21 is joined to the support member 6, and the support member 6 is joined to the inner surface of the housing 5. ing. That is, both ends in the longitudinal direction of the piezoelectric element 7 are fixed to the housing 5 via the foamed rubber 21 and the support member 6, respectively. Further, the lower surface 13 substantially at the center in the longitudinal direction of the piezoelectric element 7 is joined to the vibration film 8 via a conical coil panel as the vibration transmission member 9. A space 12 having a height of 0.3 [mm] is formed between the upper surface 10 of the piezoelectric element 7 and the ceiling surface 11 of the housing 5. The piezoelectric element 7 is manufactured by the same material and the same manufacturing method as the piezoelectric element of the first embodiment. The external dimensions of the piezoelectric element 7 are 20 [mm] in length, 4 [mm] in width, and 0.4 [mm] in thickness. The same conical coil spring 9 as the conical coil panel of the first embodiment is used. Further, the diaphragm 8 is a circular polyethylene terephthalate film having a thickness of 0.1 [mm] and a diameter of 18 [mm]. The thickness of the housing 5 is 0.3 [mm].

As can be seen from FIG. 13B, the piezoelectric acoustic device 1 of this example has a substantially circular planar shape, and has a diameter

(L) is 22 [mm]. The total height (H) is 1.5 [mm].

(Example 4)

Hereinafter, still another embodiment of the piezoelectric acoustic device of the present invention will be described. Figure 14 shows the book FIG. 1 is a longitudinal sectional view showing a schematic structure of a piezoelectric acoustic device 1 of an example. In the piezoelectric acoustic device 1 of the present embodiment, a piezoelectric device 7 of the same type as the piezoelectric device of the first embodiment is joined to the vibrating membranes 8a and 8b extending over the openings 3a and 3b formed on the upper and lower sides of the housing 5. I have. The vibrating membranes 8a and 8b stretched over the two openings 3a and 3b are a perfect circular polyethylene terephthalate film having a diameter of 10 [mm] and a thickness of 0.05 [mm]. The vibration transmitting member 9a interposed between the upper surface 10 of the piezoelectric element 7 and the vibration film 8a is a conical coil panel having a height of 0.2 [mm]. The vibration transmitting member 9b interposed between the lower surface 13 of the piezoelectric element 7 and the vibration film 8b is a conical coil spring having a height of 0.4 [mm]. The piezoelectric element 7 of this example is manufactured by the same material and the same manufacturing method as the piezoelectric element of Example 1. The external dimensions of the piezoelectric element 7 are 12 [mm] in length, 4 [mm] in width, and 0.4 [mm] in thickness. The conical coil springs as the vibration transmitting members 9a and 9b are the same as the conical coil springs of the second embodiment. Both ends of the piezoelectric element 7 are fixed to the inner surface of the housing 5 via the foamed rubber 21 and the support member 6 as in the third embodiment. The piezoelectric acoustic device 1 of this example has a substantially circular planar shape as a whole, as in the piezoelectric acoustic device of Example 3, but has a diameter (L) of 14 [mm] and an overall height (H) of 1.1 l. [mm], which is smaller and thinner than the piezoelectric acoustic device of Example 3.

(Example 5)

Hereinafter, still another embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 15 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device 1 of the present example. The piezoelectric acoustic device 1 of this example is characterized in that the piezoelectric device 7 having the structure shown in FIG. 16 is used. The piezoelectric element 7 shown in FIG. 16 has a multilayer structure (laminated structure) in which conductive layers 18 and piezoelectric material layers 19 are alternately stacked between a lower insulating layer 16 and an upper insulating layer 17. The upper and lower insulating layers 16 and 17 and the piezoelectric material layer 19 have a length of 16 [mm], a width of 4 [mm], and a thickness of 40 [xm]. The conductor layer 18 has a length of 16 [mm], a width of 4 [mm], and a thickness of 3 [zm]. Further, the piezoelectric material layer 19 has eight layers and the conductor layer 18 has nine layers (for convenience, some layers are omitted in FIG. 16). Therefore, the external dimensions of the piezoelectric element 7 are 16 [mm] in length, 4 [mm] in width, and about 0.4 [mm] in thickness. The lower insulating layer 16, the upper insulating layer 17, and the piezoelectric material layer 19 are made of lead dinoleconate titanate ceramic, and the conductor layer 18 is made of silver / palladium alloy (weight ratio 7: 3). . Further, the piezoelectric element 7 is manufactured by a green sheet method, and is fired at 1100 ° C. in the air for 2 hours. Calorie, each After a silver electrode for electrically connecting the conductor layer 18 was formed, the piezoelectric material layer 19 was polarized, and the electrode pads 20 formed on the surface of the upper insulating layer 17 were electrically connected to each other by a copper foil.

The outer shape and dimensions of the piezoelectric acoustic device 1 of the present embodiment are the same as those of the piezoelectric acoustic device of the first embodiment. That is, it has a substantially elliptical planar shape as a whole, its total length is 23 [mm], its overall height (H) is 1.5 [mm], and its overall width is 16 [mm].

(Example 6)

Hereinafter, still another embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 17 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device 1 of the present example. In the piezoelectric acoustic device 1 of this example, a metal elastic plate 15 is joined to the lower surface 13 of the piezoelectric device 7 with an epoxy-based adhesive, and one end of the elastic plate 15 supports the support member 6 on the inner surface of the housing 5. Has been fixed through. Further, the lower surface of the other end of the elastic plate 15 is joined to the vibration film 8 via a conical coil panel as the vibration transmission member 9. FIG. 18 is an enlarged view of the piezoelectric element 7 and the elastic plate 15 included in the piezoelectric acoustic element 1 of the present example. The piezoelectric element 7 has the same laminated structure as the piezoelectric element of the fifth embodiment. The length (1) is 12 [mm], the width (w) is 4 [mm], and the thickness (t) is 0.4 · mm]. Also, the elastic plate 15

1 1 1

The length (1) is 15 [mm], the width (w) is 4 [mm], and the thickness (t) is 0.2 mm. Elastic plate 15 material

2 2 2

The quality is SUS304.

[0048] The piezoelectric acoustic device 1 of the present example has a substantially elliptical planar shape as a whole similarly to the piezoelectric acoustic device of the first embodiment. The total length (L) is 23 [mm], the total height (H) is 1.7 [mm], and the total width is 16 [mm]. It is to be noted that the total height (H) is increased by 0.2 [mm] as compared with the piezoelectric acoustic element of Example 1 due to the thickness of the elastic plate 15.

(Example 7)

Hereinafter, still another embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 19 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device 1 of the present example. The piezoelectric acoustic device 1 of the present embodiment is characterized in that the piezoelectric device 7 is shorter than the piezoelectric acoustic device of the sixth embodiment. Specifically, as shown in FIG. 20, a piezoelectric element having a length (1) of 8 [mm], a width (w) of 4 [mm], and a thickness (t) of 0.4 [mm] is used.

1 1 1

7, a metal elastic plate 15 of length (1) 16 [mm], width (w) 4 [mm] and thickness (t) 0.2 [mm]

2 2 2

They are joined by a xy-based adhesive. The structure other than the piezoelectric element 7 is the same as that of the piezoelectric element of the sixth embodiment. Same as the acoustic element.

(Example 8)

Hereinafter, still another embodiment of the piezoelectric acoustic device of the present invention will be described. FIG. 21 is a longitudinal sectional view showing a schematic structure of the piezoelectric acoustic device 1 of the present example. The piezoelectric acoustic device 1 of this example is characterized in that a panel is used as a vibration transmitting member for joining the piezoelectric device 7 and the vibrating film 8. As shown in FIG. 22, this spring has a thin plate-shaped leg member 25 that connects the periphery of a disc-shaped upper member 22 having a diameter of 2 [mm] and the periphery of a ring-shaped lower member 23 having a diameter of 4 [mm]. Connected and has elasticity mainly in the direction of the arrow. The height of the panel is 0.4 [mm]. The structure other than the vibration transmitting member 9 is the same as that of the piezoelectric acoustic device of Example 1, and the overall length (L) is 23 [mm], the overall height (H) is 1.5 [mm], and the overall width is 16 [mm]. is there.

[0051] (Characteristic evaluation)

The measurement results of the characteristics of the piezoelectric acoustic element of Example 18 described above and the characteristics of the acoustic element of Comparative Example 14 will be described. First, the structure of Comparative Examples 14 to 14 will be outlined based on the drawings, and then the measurement results will be described.

(Comparative Example 1)

FIG. 23 shows a schematic structure of the acoustic element 30 of Comparative Example 1. The acoustic element 30 is a piezoelectric acoustic element. A piezoelectric element 32 identical to the piezoelectric element of the first embodiment is mounted in a casing 31 of the same dimensions and made of the same material as the casing of the first embodiment. ing. One end of the piezoelectric element 32 is fixed to the inner surface of the housing 31 via the same support member 33 as the support member of the first embodiment, and the other end is a free end. Further, a hole 35 is formed in the bottom 34 of the housing 31, and when a voltage is applied to the piezoelectric element 32, sound is emitted from the hole 35.

(Comparative Example 2)

FIG. 24 shows a schematic structure of the acoustic element 30 of Comparative Example 2. This acoustic element 30 is also a piezoelectric acoustic element and has basically the same structure as the acoustic element of Comparative Example 1. The difference is that both ends of the piezoelectric element 32 are fixed to the inner surface of the housing 31 and that a hole 35 is formed in the center of the bottom 34 of the housing 31.

(Comparative Example 3)

FIG. 25 shows a schematic structure of the acoustic element 30 of Comparative Example 3. This acoustic element 30 is also a piezoelectric acoustic element. And has basically the same structure as the acoustic element of Comparative Example 1. The difference is that a metal diaphragm 37 is attached to the free end of the piezoelectric element 32 via a connecting member 36.

(Comparative Example 4)

FIG. 26 shows a schematic structure of the acoustic element 30 of Comparative Example 4. The acoustic element 30 is an electromagnetic acoustic element having a permanent magnet 38, a voice coil 39, and a diaphragm 40. When a current is input to the voice coil 39 via the electric terminal 41, a magnetic force is generated, and the diaphragm 40 is vibrated by the generated magnetic force to generate a sound.

(Measurement result 1)

When the fundamental resonance frequencies of the piezoelectric acoustic device of Example 18 and the acoustic device of Comparative Example 14 were measured, the following results were obtained.

Example l: 443 [Hz]

Example 2: 452 [Hz] and 316 [Hz]

Example 3: 496 [Hz]

Example 4: 491 [Hz] and 320 [Hz]

Example 5: 396 [Hz]

Example 6: 276 [Hz]

Example 7: 263 [Hz]

Example 8: 370 [Hz]

Comparative example l: 1087 [Hz] or more

Comparative Example 2: 1067 [Hz]

Comparative Example 3: 1027 [Hz]

Comparative Example 4: 730 [Hz]

From the above measurement results, it can be seen that the piezoelectric acoustic device of the present invention has a wide frequency band. In particular, it can be seen that the piezoelectric acoustic elements of Example 2 and Example 4 have two fundamental resonance frequencies, and the frequency band is expanded.

(Measurement result 2)

Example 18 A voltage of 1 [V] was applied to the piezoelectric acoustic element of Example 8 and the acoustic element of Comparative Example 1 to 4. The following results were obtained when the sound pressure level was measured.

Example 1:: 96 [dB]

Example 2:: 92 [dB]

Example 3:: 91 [dB]

Example 4:: 99 [dB]

Example 5:: 107 [dB]

Example 6:: 106 [dB]

Example 7:: 118 [dB]

Example 8:: 97 [dB]

Comparative Example 1:: 38 [dB]

Comparative Example 2:: 57 [dB]

Comparative Example 3:: 74 [dB]

Comparative Example 4:: 72 [dB]

From the above measurement results, it is clear that the piezoelectric acoustic device of the present invention can reproduce a sufficiently high sound pressure. In particular, when a voltage of 0.5 [V] was applied to the piezoelectric acoustic device of Example 5, the sound pressure level was 91 [dB]. That is, despite the applied voltage of 1/2, a sound pressure of almost the same level as that of the piezoelectric acoustic elements of Examples 13 to 13 was obtained.

[0060] (Measurement result 3)

The sound pressures of the acoustic elements of Examples 1 to 8 and Comparative Examples 1 to 4 at a frequency of 500 [Hz] to 2000 [Hz] were measured, and the difference between the maximum sound pressure and the minimum sound pressure was calculated. The result was obtained.

[0061] Example 11: Within 8: 25%

Comparative Example 11: 3: Greater than 40%

Comparative Example 4: More than 25% and up to 40%

From the above measurement results, it can be seen that the piezoelectric acoustic device of the present invention has flat sound pressure frequency characteristics.

[0062] (Measurement result 4)

The piezoelectric element of Example 18 and the acoustic element of Comparative Example 14 were naturally placed 50 cm directly above. The sound pressure level was measured before and after dropping, and the rate of change was calculated. The following results were obtained.

[0063] Examples 1 and 2: Within 3%

Example 3: More than 3% and 10% or less

Example 4-17: Within 3%

Example 8: More than 3% and 10% or less

Comparative Example 1-1: greater than 10%

From the above measurement results, it is found that the piezoelectric acoustic device of the present invention has excellent impact resistance.

(Measurement result 5)

The piezoelectric acoustic device of Example 18 and the acoustic device of Comparative Example 14 were driven continuously for 100 hours, the sound pressure level was measured before and after that, and the rate of change was calculated. Obtained.

Example 1, 2: More than 3% and 10% or less

Example 3-8: Within 3%

Comparative Example 11-4: 10% or more

From the above measurement results, it is clear that the piezoelectric acoustic device of the present invention has sufficient durability and high reliability.

[0066] (Measurement result 6)

Example 18 Each of the piezoelectric acoustic device of Example 18 and the acoustic device of Comparative Example 14 were manufactured, and the sound pressure level when a voltage of 1 [V] was applied to each was measured, and the maximum value and the minimum value were measured. The following results were obtained when the deviation rate was calculated.

Examples 1 and 2: Within 5%

Example 3: Greater than 5% and within 15%

Example 4-1 7: Within 5%

Example 8: Greater than 5% and within 15%

Comparative Example 11: 4: Greater than 15%

From the above measurement results, the piezoelectric acoustic element of the present invention has little variation between products. Help.

Table 1 showing the above measurement results 116 is shown. Regarding measurement result 1, “「 ”indicates that the basic resonance frequency is 300 [Hz] or less, and“ 〇 ”indicates that the fundamental resonance frequency is greater than 300 [Hz] and 500 [Hz] or less than“ 〇 ”and 700 [Hz]. The case where the frequency is larger than 1000 [Hz] is indicated by "△", and the case where it is higher than 1000 [Hz] is indicated by "X".

[0069] Regarding the measurement result 2, the case where the sound pressure level is larger than 90 [dB] is indicated by "◎", and the case where the sound pressure level is 90 [dB] or lower is indicated by "X".

[0070] Regarding measurement results 3 and 6, "〇" indicates that the deviation rate is within 25%, "△" indicates that the deviation rate is greater than 25%, and "△" indicates that the deviation rate is 40% or less. It is represented by "X".

[0071] Regarding measurement results 4 and 5, "〇" indicates that the sound pressure change is within 3%,

The case within 10 Q / o was indicated by "△", the case larger than 10%, and the case "X".

[0072] Regarding measurement result 6, "〇" indicates that the deviation rate is within 5%, "△" indicates that the deviation rate is greater than 5% and 15% or less, and "X" indicates that the deviation rate is greater than 15%. expressed.

[0073] [Table 1]

Summarizing the previous description and measurement results 1-16, the piezoelectric acoustic element of the present invention has various advantages such as thinness, small size, low voltage drive, high sound pressure reproduction, wide frequency characteristics, low cost, and high reliability. It can be seen that Further, it can be seen that the piezoelectric acoustic device of the present invention can be applied to a wide range of fields including acoustic devices and portable terminal devices. For example, when mounted on an audio device, a small, high-quality audio device is realized. In addition, by installing the piezoelectric acoustic element of the present invention instead of the electromagnetic acoustic element mounted on a conventional mobile phone or PDA (Personal Digital Assistance), the size of the mobile phone or PDA can be reduced and the operating time can be extended. It is possible to achieve higher sound quality while planning.

[0075] Although selected embodiments of the present invention have been described using specific terms, this description is for the purpose of illustration only and departs from the spirit and scope of the following claims. It will be appreciated that modifications and variations are possible without departing from the invention.

Claims

The scope of the claims

[I] A piezoelectric acoustic element using a piezoelectric element as a vibration source,

A hollow housing having at least one opening;

A piezoelectric element that is provided inside the housing and bends when a voltage is applied, and a vibration film that is provided in an opening of the housing,

A piezoelectric acoustic element in which the piezoelectric element and the vibrating film are joined via a vibration transmitting member having elasticity.

2. The piezoelectric acoustic device according to claim 1, wherein one or both ends in the longitudinal direction of the piezoelectric device are fixed to an inner surface of the housing via a support member.

3. The piezoelectric acoustic device according to claim 2, wherein the support member has elasticity.

4. The piezoelectric acoustic device according to claim 1, comprising at least two vibrating membranes and / or vibration transmitting members having at least one of a thickness, a material, and a dimension different from each other.

5. The piezoelectric acoustic device according to claim 1, comprising two vibrating films opposed to each other with the piezoelectric device interposed therebetween, and the two vibrating films are joined to the piezoelectric device via separate vibration transmitting members.

6. The piezoelectric acoustic device according to claim 1, further comprising: an elastic plate joined to the piezoelectric element, wherein the elastic plate is joined to the vibration film via the vibration transmitting member.

7. The piezoelectric acoustic device according to claim 1, wherein the piezoelectric device has a laminated structure in which conductor layers and piezoelectric material layers are alternately stacked.

8. The piezoelectric acoustic device according to claim 1, wherein the vibration transmitting member is a panel.

9. The piezoelectric acoustic device according to claim 1, wherein the vibration film is any one of a polyethylene terephthalate film, a polyether sulfone film, a polyester film, and a polypropylene film.

[10] An acoustic device on which the piezoelectric acoustic element according to claim 1 is mounted.

[II] A mobile terminal device equipped with the piezoelectric acoustic device according to claim 1.